1. Field of the Invention
The present invention relates to a negative pressure air-lubricated bearing slider in a magnetic recording apparatus, where a magnetic transducer is installed, and more particularly, to a slider in which flying stability is improved.
2. Description of the Related Art
In a magnetic recording apparatus, a slider flies above a disc by using air as a lubricant. FIG. 1 shows the structure of a hard disc drive (HDD) as an example of the magnetic recording apparatus.
Referring to the drawing, in a driving apparatus of a hard disc drive 10, a disc 11 placed on a spindle motor 12 rotates and a negative pressure air-lubricated bearing slider 14 is attached at a suspension 15 to correspond to the magnetic disc 11. The negative pressure air-lubricated bearing slider 14 is moved by an actuator 16 which pivots so that the slider 14 moves to a desired position on a track 13 of the disc 11. The disc 11 used as a recording medium has a circular shape and different information is recorded on each track 13. Accordingly, to obtain desired information, the slider 14 moves in search of a corresponding track on the disc 11. Here, a linear velocity and skew angle change according to the position of the track 13 and accordingly the flying height, a pitch angle, a roll angle of the slider 14 are changed.
Referring to FIGS. 2A, 2B and 2C, linear velocity 25 generated due to rotation of the disc 11 changes in proportion to the radius of the disc 11 at each of the tracks having different radii. Thus, the flying attitude of the slider 14, that is, a flying height 21, a pitch angle 22, and a roll angle 23, changes according to the position of each track.
The flying height 21 means the height between the slider 14 and the disc 11 at a position where a magnetic transducer 26 for recording/reproducing information. The pitch angle 22 means an angle made by the lengthwise direction of the slider 14 and the surface of the disc 11. The roll angle 23 means an angle made by the widthwise direction of the slider 14 and the surface of the disc 11. The skew angle 24 means an angle made by a tangent of a track of the disc 11 and a lengthwise direction 15 of the slider 14. The skew angle 24 greatly affects generation of pressure to a bearing so that the flying attitude, that is, the flying height 21, the pitch angle 22, and the roll angle 23, changes much according to the radius of the disc 11.
Since about 2-3 micro inches or more is conventionally required for the flying height, even when the amount of a change in the flying height is somewhat great, such a change does not affect recording and reproducing of information. However, as the flying height is recently lowered to 1 micro inch or less, the range of a change in the flying height becomes small and stable flying is needed. When the range of a change in the flying height is great, recording and reproducing of information is difficult and collisions between the slider and the disc are frequently made so that durability and reliability of the whole system are lowered.
The relationship between a head writing field (Hw) and the coercivity (Hc) of a recording medium is expressed by the following equation.
Hw=axc3x97Hcxe2x80x83xe2x80x83[Equation 1]
In Equation 1, when it is assumed that the coercivity of a recording medium fixed, the size of the head writing field is determined by a value a. As the value a decreases, the head writing field is reduced. This means that a head with a small writing field can sufficiently record information on a recording medium. The value a is related to the flying height that is a gap between the slider and the disc. Thus, the value a can be reduced by reducing the flying height. When the flying height is lowered, the size of bits related to a recording density is reduced so that a greater amount of information can be stored.
While the recording density increases as the flying height is lowered, the possibility that the slider collides with the disc by external interferences such as an outside impact, increases. To prevent this problem, various slider shapes have been suggested.
FIG. 3 shows the structure of a slider having a conventional shape which is disclosed in U.S. Pat. No. 3,823,416, which is the same as those shown in FIGS. 2A, 2B and 2C.
Referring to FIG. 3, rails 31a each having a taper 32a are formed at both sides on the bottom surface of a slider parallel to each other in the lengthwise direction. The slider having this shape is basically used in an initial form of a magnetic recording apparatus, and is named a taper flat (TF) slider. This slider is disadvantageous in that the flying height, the pitch angle, and the roll angle change very greatly with respect to changes in the disc linear velocity and the skew angle which are described above with reference to FIGS. 2A, 2B, and 2C. Since a magnetic transducer 26 is disposed at the rear of one rail at the back of the slider, the flying height is greatly affected by not only a change in the pitch angle, but also a change in the roll angle, so that it is difficult to maintain a constant flying height with respect to the radius of a disc.
The reasons for using the taper flat slider in spite of the above problems are as follows. First, since a linear actuator is mainly used instead of a rotary actuator, there is no need to consider an effect by the skew angle. Second, since the flying height is 4 micro inches or more, even when the amount of a change in the flying height with respect to the radius of a disc is large, recording and reproducing of information are not affected much.
FIG. 4 shows the structure of a slider which is disclosed in U.S. Pat. No. 5,473,485. Referring to the drawing, rails 31b each having a taper 32b at the front side of the slider are formed at both sides on the bottom surface of the slider to the middle portion of the slider. A pad 33b is formed in the middle of the rear side of the slider. The slider having the above structure is named a tri-pad slider and exhibits a stable flying attitude compared to the conventional taper flat slider.
However, as a need for a high density recording apparatus increases, the flying height between the slider and the disc is drastically reduced to 2 micro inches or less. A slider for generating negative pressure which enables a stable flying attitude with respect to the external interferences has been suggested.
FIG. 5 shows a negative pressure air-lubricated bearing slider disclosed in U.S. Pat. No. 3,855,625 which is named a zero-load slider.
Referring to FIG. 5, rails 31c are formed at both sides on the bottom surface of a slider parallel to each other. A bridge 35c is formed at the middle portion between both rails 31c to section the space between both rails 31c into a positive pressure space portion 33c and a negative pressure space portion 34c. 
The feature of the negative pressure slider having the above structure is as follows. Positive pressure that lifting the slider above the disc is generated at the positive pressure space portion 33c. Negative pressure corresponding to the positive pressure is generated at the negative pressure space portion 34c between air-bearing surfaces (ABS). According to the above structure, a suction force toward the disc is generated to the slider due to the negative pressure generated at the negative pressure space portion 34c so that great stiffness of an air bearing is formed while having light external load. However, in such a negative pressure slider, since the amount of a change in the roll angle is greatly generated according to a change in the skew angle, the flying height at the position where a magnetic transducer 26 is installed is much affected so that recording/reproducing is not performed properly. Also, in the case, in which a change with respect to roll, such as, track seek motion or lamp loading, is great, dynamic stability in a direction of rolling is lowered.
To obtain a stable flying feature, the following conditions are required to be met.
First, the flying height must be maintained to be constant with respect to the radius of a disc. That is, the flying height of a slider should not be changed regardless of a change in the speed of air flow and a skew angle in the entire area of a disc from the inner side to the outer side of the disc. As the flying height is recently very low (less than 1 micro inch), this condition should be sternly met
Second, the size of a pitch angle made by the slider should be included within a proper range regardless of the radius of the disc. If the pitch angle is too small, a crash that is a collision between the front portion of the slider and the disc, is generated, resulting in severe damage to the disc. Also, a sufficient wedge effect is not obtained so that a dynamic stiction, in which the slider is sucked to the disc during the operation, is generated. When the pitch angle is too great, the stiffness of an air bearing is not sufficiently maintained so that the dynamic stability of the slider is lowered.
Third, the change in the roll angle of the slider within the entire area of the disc in the radial direction should be small. Since the flying height is measured at the center of the rear of the slider, the flying height is not changed much by the roll angle. However, considering track seek and dynamic stability in a roll direction with respect to the external moment in the roll direction, the roll angle should always be a stable small value.
Fourth and the last, by providing a shape which enable negative pressure to be generated in a sufficient amount, the stiffness of an air bearing is maximized. To minimize a change in the flying height with respect to an error in assembly of a magnetic recording apparatus, an error in the size of suspension load, and an error in manufacturing the air bearing surface, the stiffness of the air bearing should be maximized.
To solve the above problems, it is a first object of the present invention to provide a negative pressure air-lubricated bearing slider in which the flying height is maintained uniformly in the entire area of a disc.
It is a second object of the present invention to provide a negative pressure air-lubricated bearing slider in which the pitch angle is maintained within an appropriate range in the entire area of a disc.
It is a third object of the present invention to provide a negative pressure air-lubricated bearing slider in which the size of a roll angle is minimized in the entire area of a disc.
It is a fourth object of the present invention to provide a negative pressure air-lubricated bearing slider which provides dynamic stability with respect to the outer interference and the track seek.
It is a fifth object of the present invention to provide a negative pressure air-lubricated bearing slider which minimizes the amount of contaminant particles intruding into a head-disc interface (HDI) and effectively prevents accumulation of the intruding contaminant particles in a negative pressure space portion.
Accordingly, to achieve the above objects, there is provided a negative pressure air-bearing slider comprising a body flying in a first direction along a track of a disc where information is recorded while being raised to a predetermined height, a plurality of rails provided at the bottom of the body corresponding to a surface of the disc, an air inflow channel arranged at the bottom of the body in the first direction and having an air inflow portion at the leading end portion of the slider and an air exhaust portion at the inside of the body, and a pair of negative pressure recess portions provided at the air exhaust portion of the air inflow channel to be arranged in a second direction perpendicular to the first direction with respect to the air inflow channel.
It is preferred in the present invention that a first rail base having a W shape which is disposed at the front side of the slider in the first direction, encompassing the negative pressure recess portion pair, and having a protruding portion extending between the negative pressure recess portions at the center of the slider, and the first rail corresponding to each of the negative pressure recess portions is provided on the first rail base.
It is preferred in the present invention that an upper surface of the protruding portion is disposed lower than the first rail, and the air inflow channel is provided at the upper surface of the protruding portion.
It is preferred in the present invention that the first rail is formed on a portion of the upper surface of the first rail base, and a front stepped portion is provided at the upper surface of the first rail base at the leading end portion of the first rail.
It is preferred in the present invention that the first rail is formed on a portion of the upper surface of the first rail base, and a rear stepped portion is provided at the upper surface of the first rail base in the rear of the first rail facing the negative pressure recess portions.
It is preferred in the present invention that a second rail base is provided in the rear of each of both sides of the first rail base at a constant interval, and a second rail is provided at each of the second rail bases.
It is preferred in the present invention that a third rail is provided between the second rails.
It is preferred in the present invention that the second rail is separated a predetermined distance from the read end of the body.
It is preferred in the present invention that an inclined portion is formed at each corner of both sides of the front side of the first rail base.
According to another preferred embodiment of the present invention, to achieve the above objects, there is provided a negative pressure air-bearing slider comprising a body, a first rail, provided at the leading end portion of the body in a first direction, having a pair of first portions arranged at both sides in the first direction, a second portion in a second direction of which both ends are connected to the leading end portions of the first portions, and an air inflow channel in the first direction provided at the central portion of the second portion, in which a pair of negative pressure recess portions are provided at both sides in the second direction at a predetermined interval with respect to the air inflow channel in an inner space between the first portions and the second portions, and a pair of second rails provided at both sides of the rear of the body of the slider in the first direction.
It is preferred in the present invention that a third rail disposed at the central portion of the rear side in the first direction is interposed between the second rails.
It is preferred in the present invention that the first rails have a protruding portion having a predetermined height at the middle portion thereof and are formed at both sides of a first rail base having a W shape and encompassing the negative pressure recess portions, and the air inflow channel is provided on the upper surface of the protruding portion of the first rail base.
It is preferred in the present invention that the first rail is formed on a portion of the upper surface of the first rail base, and a stepped portion is formed by the upper surface of the first rail base where the first rail is not formed at any of the front and rear sides of the first rail.
It is preferred in the present invention that the length of the protruding portion has a value not more than 70% of the length of the body.